SAN FRANCISCO — The Trump administration on Monday threw out a new rule intended to limit the numbers of endangered whales and sea turtles getting caught in fishing nets off the West Coast, saying existing protections were already working.

Economically, the new rule would have had “a much more substantial impact on the fleet than we originally realized,” said Michael Milstein, a spokesman with the federal fisheries service, which killed the rule.

The rule would have applied to fewer than 20 fishing vessels that use mile-long fishing nets to catch swordfish off California and Oregon. The change would have shut down the drift gillnet fishing for swordfish for up to two seasons if too many of nine groups of whales, sea turtles or dolphins were getting caught in the nets.